fwupdmgr has a firmware upgrade for the laptop in question (AMD Framework 13), titled System Firmware (0.0.3.2 → 0.0.3.3). The 0.0.3.2 version's issues with graphics drivers are well documented by the vendor; I would swear that this was already installed, but apparently not. On doing this update, everything appears to work fine.
Welp, now we know I guess. Thanks. --
